Agitator for vacuum still



March 5, 1957 A. Rosi: ETAL AGITATOR FOR VACUUM STILI.

INVENTORS ARTHUR ROSE WILLIAM W. SANDERS ATTORNEY United States Patent AGITATOR FOR VACUUM STILL Arthur Rose and William W. Sanders, State College, Pa., assignors to the United States of America as represented -by the Secretary of Agriculture "Application september 16, 195s, serial No. 380,627

z claim.- (ci. 2oz-17s) This invention relates to means for the agitation of the liquid phase in the boiler of a still adapted for operation at subatmospheric pressure,

i An object of thisninvention isto provide an improved agitator Yfor usein vacuum stills. Another object is to provide means `for preventing bumping 'of the' liquid in the boiler of vacuum stills. A further object is to promote quiet, steady equilibrium evaporation from the liquid phase in the boiler of vacuum stills. A still further object is to provide an agitator which is entirely 'sealed within the apparatus but which may be operated by means of external energy sources.

The term bumping as understood in the art, means the sudden, violent, irregular evolution of vapor from a hot liquid. Bumping may be encountered in the boiling of any liquid and is particularly troublesome in the distillation of viscous, high-boiling substances, especially if the distillation is carried out under vacuum. Bumping is espe'- cially objectionable in fractional distillations in vacuum because the sudden irregular surges of super-heated vapor evolved from the boiler upset the vapor-liquid equilibrium in the fractionating column and hence impair the efliciency of the fractionation.

To prevent the foregoing ditiiculties, we Ihave invented the agitator described below for use in vacuum distillations which is effective at all pressure-s and with liquids of high viscosity, which requires no sealing gasket, packing, or lubricant, and which can be constructed entirely of noncorroding material. The agitator is actuated by an cxternal solenoid, thus dispensing with the need for packing glands, seals, bearings, or lubricants.

A preferred embodiment of our novel agitator is described in the following specification, reference being made to the accompanying drawings. Similar reference numerals refer to like parts in the several views.

In the drawings:

Figure 1 shows a vertical section through a ycomplete assembly of a still boiler Iand includes the details of our novel agitator unit.

Figure 2 is a plan view of one of the agitator baies.

In a preferred embodiment of our invention, the agitator comprises a solid glass rod or shaft 1 having a plurality of cup shaped -batlies 2 attached at intervals along its length. These bafles are arranged with their concave sides down and are provided with a number of holes 3 around their surfaces. Fused to the upper end of rod 1 is a length of glass tubing 4 in which is sealed a soft iron armature 5. At the lower end of the solid glass rod there is fused another length of glass tubing 6, around" which iswound a bumper spring 7, which is made of a non-corroding material, such as, stainless steel wire. In order to secure the spring to the stirrer, 'both ends of the wire are passed through a hole 8 in the tube 6, and several turns taken around the tube. The baflies are secured to the glass rod by fusing short pieces of rod to the s, and then fusing the ends of these short rods together toa continuous length. i

2,784,150 Patented Mar. 5, 1.957

In use, the stirrer is mounted vertically in a still pot 9, as shown in Figure 1, of such size that the liquid level 10 in the pot fallson that part of the rod4 or shaft 1 on which the batlies are disposed when the spring bumper 7 rests on the bottom of the pot. The boiler is provided with two necks 11 and 12, each having a spherical ground joint 13 and 14, respectively, at its end. Neck 12 is connected' to tube 15, the lowe'r'end of which'is ground to mate with joint 14, and the upper end of which is sealed. `A glass wool pad 16 is inserted and secured in the upperend of tube 15. To the other neck 11 there is attached another tube 17 which conducts the distilled vapors to a condenserl or a fractonating column, not shown. Both spherical joints 13 and 14 are held together by means of conven-I tional clamps, not shown, available for thepurpose To operate the stirrer'a' solenoid 18 is placed around the upperend of tube 15, andso adjustedin position that, when intermittently "energized, it will alternately `liftjand drop the stirrer by means of the soft iron armature 5 with' a vertical reciprocating motion.l This-'motion should liar/"ev suflicient amplitude to assure that at least one of tlige baffles on the stirrer shaft passes through the liquid surface. Oni the upstroke this breaks the surface and splashes the liquid, and also exerts a pumping action whereby circulation within the body of liquid is favored. On the downstroke the bal-e or baies that pass through the liquid surface not only exert a splashing and pumping effect, vbut also carry trapped vapor below the surface. This vapor gradually escapes as a train of,bubbles from the perforatioi'is in the baie. These bubbles act as nuclei for evolution of vapor from the boiling liquidr and thus help avoid superheating and bumping. Y v

The time cycle during which the solenoid is energized and de-energized, andjduring which the stirrer makes one upward and one downward stroke, may be variedfwidely, 'but we have found that a frequency of from 501to 150 cycles per minute gives best results with most liquids. 1t is apparent that, if the frequency is too low, there will be superheating and bumping of the liquid between strokes ot' the stirrer. On the other hand, if the frequency is too high, the stirrer will not have time to make a fullstroke and will vibrate with `too small an amplitude. Thus, the optimum frequency will depend upon the -size of the apparatus, the depthand viscosity of the liquid, and the rate of distillation; but it is easily determined in practice.

The purpose of the spring bumper on the lower end of our stirrer and the glass wool fabric above the upper end l is to cushion the strokes of the stirrer and preventbreakage where the stirreror the still pot, or both, are made of glass. It will be apparent, however, that our invention is not limited to the use of glass apparatus but any of the structural materials commonly used in industry may be substituted; nor is it necessary to use spherical joints. Any joint capable of holding a vacuum or high pressure may be used instead. lf neither the'stirrer nor the still pot is made of glass then the glass fabric pad and spring may be dispensed with; although the spring bumper also has some advantageous effect in that its resiliency helps start the stirrer on its upward stroke and thus promotes smooth operation. If the time cycle on which the stirrer is actuated corresponds to the natural frequency of the. spring as loaded, a harmonic oscillation of the stirrer is set vup and operation of the assembly is particularly smooth and efficient.

Any conventional timer having a suit-able on-of cycle may be used in the solenoid circuit, although in the interest of adaptability it is highly desirable that its time cycle be adjustable.

We claim:

1. A vacuum still' capable of equilibrium evaporation with no bumping comprising a still pot having two necks, one of said necks being connected to a longitudinally ex- 'tended mee losen .ai as .fsf end, :he seem: @issie seeks being connected to condensing means; the Yfirst of said necks and its attached tube having extending therein an agitator comprising an elongated shaft having disposed along its midsection in a .spaced relationship .-a plurality of inverted cup-shaped bailles, each baffle having n plurality of perforations spacedly -disposed,over it-ssurface, ,said shaft passing through `the center of, and being rigidly attached to, :each baille, `said shaft further having att-ached to its lower end 'an open-spiral elastic spring and to its upper end a totally enclosed chamber containing a soft iron core; the aforementioned tube attached to the first neck Ibeing surrounded near vits upper end by a solenoid capable of imparting a vertically reciprocating motion Vto the enclosed agitator when `said solenoid is cyclical'ly activated and `deactivated by passage of electric current therethrough.

2. A vacuum still capable of equilibrium evaporation with no bumping comprising a still pot having two necks, one of said necks lbeing connected to condensing means; the second of said necks having an upwardly vextending tube attached thereto, said tube being sealed at its upper end and having disposed therein an agitator comprising ,an elongated shaft extending substantially to the bottom of the still pot, a plurality of cupshaped -baies rigidly `attached to the shaft in spaced relationship to each other with their open concave sides downward, the shaft passing jtlrrotfighthe center-1 of each nfiasiaidlbatiies, eachbattle having disposed over its surface a plurality of small perforations, an'elastic Vspring secured to the lower end of the shaft, and means to impart to said shaft a reciprocating motion parallel to the long axis of the shaft.

References Cited in the le of this patent UNITED STATES PATENTS 6,133 Y Murdock Feb. 20, 1849 99,883 Haines Feb. .15, 1870 s 1,176,953 Fritz Mar. 28, 1916 A1,745,177 Markley Jan. 28, 1'9'30 1,962,275 v Holst et al June 12, 1934 2,128,544 mrianino Ang.`30, V1938 2,142,961 Kuhn l Jan. 3, 1939 2,149,987 Altorfer" Mar. 7, 1939 2,235,094 Walker Mar. 18, 1941 2,242,812 Brown May 20, 1941 2,356,573 `'Dunham Aug. 22, 1944 '2,425,691 Brewer Aug. 112, 1947 2,471,876 Kuhn May 31,' 1949 2,498,212 Laverell et al. Feb. .21, 1950 2,635,949 Fenske et al Apr. '21, 1953 2,661,938 Knentzei Dec; 8, 1953 

1. A VACUUM STILL CAPABLE OF EQUILIBRIUM EVAPORATION WITH NO BUMPING COMPRISING A STILL POT HAVING TWO NECKS, ONE OF SAID NECKS BEING CONNECTED TO A LONGITUDINALLY EXTENDED TUBE CLOSES AT ITS FAR END, THE SECOND OF SAID NECKS BEING CONNECTED TO CONDENSING MEAND; THE FIRST OF SAID NECKS AND ITS ATTACHED TUBE HAVING EXTENDING THEREIN AN AGITATOR COMPRISING AN ELONGATED SHAFT HAVING DISPOSED ALONG ITS MIDSECTION IN A SPACED RELATIONSHIP A PLURALITY OF INVERTED CUP-SHAPED BAFFLES, EACH BAFFLE HAVING A PLURALITY OF PERFORATIONS SPACEDLY DISPOSED OVER ITS SURFACE, SAID SHAFT PASSING THROUGH THE CENTER OF, AND BEING RIGIDLY ATTACHED TO, EACH BAFFLE, SAID SHAFT FURTHER HAVING ATTACHED TO ITS LOWER END AN OPEN-SPIRAL ELASTIC SPRING AND TO ITS UPPER END A TOTALLY ENCLOSED CHAMBER CONTAINING A SOFT IRON CORE; THE AFOREMENTIONED TUBE ATTACHED TO THE FIRST NECK BEING SURROUNDED NEAR ITS UPPER END BY A SOLENOID CAPABLE OF IMPARTING A VERTICALLY RECIPROCATING MOTION TO THE ENCLOSED AGITATOR WHEN SAID SOLENOID IS CYCLINICALLY ACTIVATED AND DEACTIVATED BY PASSAGE OF ELASTIC CURENT THERETHROUGH 